CHAPTER 11 A&P

CNS phagocyte

microglial cell

may be involved in exacting types of mental activity

parallel after-discharge

what factors appear to guide the outgrowth of an axon and it's ability to make the correct synaptic contacts

The growth cone at the tip of an extending axon is exquisitely sensitive to repulsive and attractive guidance cues in its environment. These molecules may be diffusible and work from a distance, or may be bound to a membrane or substrate and work at close range. It is the complex integration of these repulsive and attractive signals that enhance or suppress axon outgrowth, and/or guide the axon to its appropriate target. These molecules play critical roles during nervous system development and may regulate the regeneration during nervous system disease.

which of the following structures is not part of the central nervous system

a nerve

assume that an EPSP is being generated on the dendritic membrane. Which will occur

a single type of channel will open, permitting simultaneous flow of Na+ and K+

biogenic amine neurotransmitter a include all but

acetylcholine

many neurons influence few neurons

converging

one or few inputs ultimately influence large numbers of neurons

diverging

the neuropeptides that act as natural opiates are

enkephalins

lines brain cavities

ependymal cell

the velocity of nerve impulse conduction is the greatest in

heavily myelinated, large-diameter fibers

chemical synapses are characterized by all of the following except

ions flowing through protein channels from the pre synaptic to the post synaptic neuron

An IPSP is inhibitory because

it hyper polarized the post synaptic membrane

myelinated nerve fibers in the central nervous system

oligodendrocyte

impulses continue around and around the circuit until one neuron stops firing

reverberating

most abundant, help regulate the ionic composition of CNS extracellular fluid, play a role in capillary-neuron exchange& controls chemical environment around neurons

astrocyte

the anatomical region of a multipolar neuron that has the lowest threshold for generating an AP is the

axon hillock

what type of current flows through the axolemma during the steep phase of re-polarization

chiefly a potassium current

(a) contrast unipolar, bipolar, and multipolar neurons structurally (b) indicate where each is most likely to be found

A unipolar neuron is a type of neuron in which only one protoplasmic process (neurite) extends from the cell body. Most neurons are multipolar, generating several dendrites and an axon and there are also many bipolar neurons. Bipolar neuron= A neuron that has two processes arising from opposite poles of the cell body. A multipolar neuron (or multipolar neurone) is a type of neuron that possesses a single (usually long) axon and many dendrites, allowing for the integration of a great deal of information from other neurons. These dendritic branches can also emerge from the nerve cell body.

inhibition of acetylcholinesterase by poisoning blocks neurotransmission at the neuromuscular junction because

ACh is not degraded, hence prolonged depolarization is enforced on the post-synaptic cell

describe the events that must occur to generate an action potential. Relate the sequence of changes in permeability to changes in the ion channels, and explain why the action potential is an all or none phenomenon

As sodium ions diffuse inward, the membrane loses its negatively electrical charge, and becomes depolarized. At almost the same time, however, membrane channels open that allow potassium ions to pass through and as these positive ions diffuse outward, the inside of the membrane becomes neagatively charged once more. Thus, the membrane returns to the resting potential, and it remains in this state until stimulated again. This rapid sequence happens within about one thoundseth of a second

briefly describe the three stages of neuron devopment

Bastula Stage- the embryo rapidly divides (cleavage) and forms a cavity called the blastocoel. GASTRULA STAGE-migration of the mesoderm (IMZ) towards the inside of the embryo (the migrating cells will form the notochord) NEURULA STAGE-the neural plate (future central nervous system -CNS), becomes visible in dorsal ectoderm5.

what is the polarized membrane state? how is it maintained?

Because the voltage across a neural membrane is approximately -70mv, the inside of the membrane is negatively charged compared to the outside

(a) explain the difference between an EPSP and an IPSP (b) what specifically determines whether an EPSP or IPSP will be generated by at the post synaptic membrane?

ESPS- the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels IPSP- the flow of negative ions into the cell or positive ions out of the cell The specific transmitter released in the synapse determines whether or ESPS or IPSP will result in the polysynaptic membrane

In the Netherlands a young man named Jan was admitted to the emergency room. He and his friends had been to a rave. His friends say he started twitching and having muscle spasms which progressed until he was "stiff as a board." On examination, staff found a marked increase in muscle time and hyperreflexia involving facial and limb muscles. In his pocket, he had unmarked dark yellow tablets with dark flecks. Analysis of the tablets showed them to contain a mixture of ecstasy and strychnine. Ecstasy would not cause this clinical picture, but strychnine, which blocks glycine receptors, could. Explain how.

Glycine is an inhibitory neurotransmitter that is used to modulate spinal cord transmission. Stlychnine blocks glycine receptors, leading to unregulated stimulation of muscles, and spastic contraction to the point where muscles cannot relax.

Distinguish between serial and parallel processing.

In visual search, both serial and parallel are used to describe performance in search tasks with lots of distractors. The idea is that with a parallel search, the time you take to find the target doesn't depend on how many things are there. If I ask you to find a red dot amongst black dots, you won't be any slower if there are 20 dots overall vs if there are 5, because you basically processes them all at once. If its distinguished by a single feature (though it doesn't work for all feature types), it 'pops out', a term used a lot in the literature.

since all action potentials generated by a given nerve fiber have the same magnitude, how does the CNS know whether a stimulous is strong or weak?

It determines by the frequency of the signals that arrive from the peripheral nervous system as opposed to determining by the strength of the signal. The action potential that travels along the neurons is always the same strength, but if the stimulus is strong it will fire the action potential more frequently.

Rochelle developed multiple sclerosis when she was 27. After eight years she had lost a good portion of her ability to control her skeletal muscles. How did this happen?

Multiple sclerosis destroys myelin sheaths. This loss means gaps are excited more slowly & conduction ceases. Without consistent innervation, skeletal muscles become weak, clumsy, and paralyzed.

(a) what is myelin? (b) how does the myelination process differ in the CNS & PNS

Myelin sheath is a fatty covering around long axons that protect it and help increase the speed of nerve impulse transmission. In the CNS the oligodendrocytes form the myelin sheath, while in the PNS Schwann cells form it. Schwann cells create gaps, known as nodes of Ranvier, while oligodendrocytes completely cover the axon.

since at any moment a neuron is likely to have thousands of neurons releasing neurotransmitter a at it's surface, how is neuronal activity (to fire or not) determined?

Once a stimuli has reached a certain threshold the neuron will fire, this is achieved through either graded potential signals or action potential signals.

myelinates nerve fibers in the peripheral nervous system

Schwann cell

during a neurobiolog lecture, a professor repeatedly refers to group A and group B fibers, absolute refractory period, and myelin sheath gaps. Define these terms.

The absolute refractory period is the interval during which a second action potential absolutely cannot be initiated, no matter how large a stimulus is applied. A fibers- myelinated afferent or efferent fibers of the somatic nervous system having a diameter of 1 to 22 μm and a conduction velocity of 5 to 120 meters per second; they include the alpha, beta, delta, and gamma fibers. B fibers- myelinated preganglionic autonomic axons having a fiber diameter of ≤ 3 μm and a conduction velocity of 3 to 15 meters per second; these include only efferent fibers. The glial cells forming myelin sheaths are called oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. The gaps (approximately 1 micrometer wide) formed between myelin sheath cells long the axons are called Nodes of Ranvier.

When admitted to the emergency room, John was holding his right hand, which had a deep puncture hole in his palm. He explained that he had fallen on a nail while exploring in a barn. John was given an anti-tetanus shot to prevent neural complications. Tetanus bacteria fester in deep, dark wounds, but how do their toxins travel in neural tissue?

The bacteria remain in the wound, but the toxins they produce travel via axonal transport to reach the cell body.

the effects of neurotransmitter binding are very brief. Explain

The binding is designed to be brief so that another one can be initiated if needed. Failure of the neurotransmitter to break down can be dangerous

(a) describe the composition and function of the cell body (b) how are axons and dendrites alike? in what ways (structurally and functionally) do the differ

The nerve cell body contains the nucleus, rough ER (Nissl bodies), and cytoplasm. It is the major biosynthetic center and the main body for the outgrowth of neuronal processes. Axons and Dendrites are both arm-like extensions from the cell body. Dendrites are short and extremely branched processes that function as the input regions of neurons. Axons are long branched processes that contain end bulbs, these bulbs secrete neurotransmitters, so axons function as the output.

Explain both the anatomical and functional divisions of the nervous system. Include the subdivisions of each

The nervous system's function is to monitor stimuli occurring inside and outside the body, process and interpret this sensory input, and respond by activating effector organs. It consists of the Central Nervous System (brain and spinal cord), and the Peripheral Nervous System (neurons that carry messages to and from the CNS).

Local anesthetics block voltage-gated Na+ channels. General anesthetics are thought to activate chemically gated Cl- channels, thereby rendering the nervous system quiescent while surgery is performed. What specific process do anesthetics impair, and how does this interfere with nerve impulse transmission?

They impair impulse propagation. This interferes with nerve impulse transmission because not enough Na+ enters the cell which equals no minimum threshold which overall equals no action potential. Also when Cl- enters cell that equals hyperpolarization which also results in no action potential.

Mr.Miller is hospitalized for cardiac problems. Somehow, medical orders are mixed up and Mr.Miller is infused with a K+ enhanced intravenous solution meant for another patient who is taking potassium-wasting diuretics. Mr.Miller's potassium levels are normal before the IV is administered. What do you think will happen to Mr.Millers resting membrane potentials? His ability to generate action potentials?

This would depolarize the resting membrane potential. The depolarization of the resting membrane would increase the generation of the action potential.